Thermoplastic composition comprising a CO2 releasing material

ABSTRACT

A composition comprising a thermoplastic and a CO 2  releasing material; wherein the CO 2  releasing material comprises: a) a carbon and oxygen containing salt of an alkali or alkaline earth metal; and b) an acid; the CO 2  releasing material has a sufficient amount and ratio of the carbon and oxygen containing salt of the alkali or alkaline earth metal and the acid so that, in the presence of water, the CO 2  releasing material reacts to release CO 2  gas through the thermoplastic into a surrounding environment.

CROSS-REFERENCE TO RELATED CASES

[0001] This application is a continuation-in-part of U.S. Ser. No.10/033,973, filed Dec. 19, 2001. This application also claims thebenefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No.60/452,004, filed Mar. 5, 2003.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0002] The present invention relates to a CO₂ releasing compositioncomprising a combination of a CO₂ releasing material that isincorporated within a thermoplastic. In the presence of water, the CO₂releasing material reacts to release CO₂ gas through the thermoplasticinto the surrounding environment.

[0003] Suitable thermoplastic materials include, but are not limited to,polyolefins such as polypropylene and polyethylene, polyisoprene,polybutadiene, polybutene, polysiloxane, polycarbonates, polyamides,ethylene-vinyl acetate copolymers, ethylene-methacrylate copolymer,poly(vinyl chloride), polystyrene, polyesters, polyanhydrides,polyacrylianitrile, polysulfones, polyacrylic ester, acrylic,polyurethane and polyacetal, or copolymers or mixtures thereof. It isunderstood that the desired thermoplastic is selected based on theend-use. For example, the specific thermoplastic selected may be basedon the desired level of gas permeability so as to allow the desiredlevel of moisture into the thermoplastic and/or the desired amount ofCO₂ gas out of the thermoplastic. In another example, the desiredthermoplastic may be selected that has the desired end-use properties ofthe shaped article (e.g. tensile strength, moldability, elasticity,cost).

[0004] In yet a further embodiment, the CO₂ releasing material may be acarbon and oxygen containing salt of an alkali or alkaline earth metal,such as the carbonates of sodium, potassium, magnesium, or calcium.Bicarbonates of the same may also be employed. In yet a furtherembodiment, the CO₂ releasing material is calcium carbonate. In yet afurther embodiment, the CO₂ releasing material may be baking powder.Mixtures of CO₂ releasing compositions are also possible.

[0005] In an embodiment of the composition, the CO₂ releasing materialloading level is between about 10% to about 80%, more specifically fromabout 10% to about 20%, about 20% to about 40%, about 40% to about 60%,and/or about 60% to about 80% by weight with respect to composition.

[0006] In another embodiment, the CO₂ releasing material may be acombination of a carbonate with an acid. Suitable carbonates include,but are not limited to, such as, but not limited to, sodium bicarbonateand/or calcium carbonate. Suitable acids include, but are not limitedto, citric acid, maleic acid, malic acid, fumaric acid, polyacrylicacid, oxalic acid and/or mixtures thereof. In one specific embodiment,the acid can be used in an anhydrous form to prevent the reaction fromoccurring prematurely. In yet another embodiment, to reduce thepossibility of the reaction initiating prematurely, the acid is in itssolid granular form and is substantially free of moisture.

[0007] In one embodiment, the CO₂ releasing material in the CO₂releasing composition is a activated by moisture and thus, results inthe controlled release of CO₂. As such, the composition including thethermoplastic and CO₂ releasing material may be designed (e.g. theamount and/or morphology) to produce the desired amount of CO₂ releaseper unit time based on the desired environment.

[0008] The CO₂ releasing composition may be produced in any desiredform. Suitable forms include, but are not limited to, film, sheets,inserts (e.g. tape strips, tabs) and liners. The following examples aremerely exemplary and are not meant to limit the application of thepresent invention. For example, the composition of the present inventionmay be formed into an insert for inclusion within the interior of thepackage. An example of one form of an insert is a plug, tab, strip,patch or sleeve of any suitable shape. In another embodiment, a linermay be formed from the composition of the present invention that has anexterior surface substantially conforming to at least a portion of aninterior surface of the package. In yet another embodiment, thecomposition of the present invention may be used to form a film orsheet. In one example, the sheeting of the present invention may bejoined with another sheet. In at least one embodiment, the sheets areeffectively laminated one to the other so that an exterior layer may beestablished adjacent to the composition of the present invention whichis substantially gas impermeable. The laminate sheet may then be used towrap an item which is to be stored in a controlled environment. Onemeans by which the joinder process may be accomplished is through athermal extrusion procedure.

[0009] The desired article may be produced by any conventional processof making a plastic article that includes, but is not limited to,extrusion, melt inflation (e.g. blown film, blow moulding,thermoforming) and/or injection molding. At some stage of the process,the CO₂ releasing material is blended with the thermoplastic and theresulting blend is subsequently processed into the desired shapearticle.

[0010] The following are merely illustrative examples of variouscompositions of the present invention. It is understood that these aremerely illustrative examples and are not meant to limit the presentinvention. Formulation Number Materials Wt percentage 001 B1H4E Resin95.00% PolyOx 750 5.00% 002 CaCO₃ 50.00% Luviskol VA64 7.00% Carbopol971 P-NF 13.00% EXACT 4023 30.00% 003 CaCO₃ 40.00% Luviskol VA64 10.00%Molecular Sieve 4A 15.00% EXACT 4023 35.00% 004 NaHCO₃ 35.00% PolyOx 7505.00% Carbopol 971 P-NF 25.00% EXACT 4023 35.00% 005 NaHCO₃ 32.00%Citric Acid 28.00% PolyOx 750 5.00% EXACT 4023 35.00% 006 NaHCO₃ 37.00%Malic Acid 37.00% PolyOx 750 5.00% EXACT 4023 21.00% 007 NaHCO₃ 50.00%Malic Acid 25.00% PolyOx 750 5.00% EXACT 4023 20.00% 008 NaHCO₃ 37.00%Malic Acid 37.00% 15-200 5.00% EXACT 4023 21.00% 009 NaHCO₃ 37.00% MalicAcid 37.00% Luviskol Va64 5.00% EXACT 4023 21.00% 010 Calcium Carbonate37.00% Malic Acid 37.00% Pluronic F108 5.00% EXACT 4023 21.00% 011NaHCO₃ 35.00% Malic Acid 35.00% PolyOx 750 10.00% EXACT 4023 20.00% 012NaHCO₃ 37.00% Malic Acid 37.00% EXACT 4023 26.00% 013 CaCO₃ 35.00% MalicAcid 38.90% PolyOx 750 5.00% EXACT 4023 21.10% 014 CaCO₃ 35.00% MalicAcid 38.90% PolyOx 750 5.00% PP 3305 21.10% 015 CaCO₃ 35.00% Citric Acid37.10% PolyOx 750 5.00% EXACT 4023 22.90% 016 CaCO₃ 37.00% Citric Acid31.00% PolyOx 750 5.00% Calcium Hydroxide (anhydrous) 6.00% EXACT 402321.10%

[0011] The following examples illustrate the use of the present CO₂releasing composition in the presence of moisture that activates the CO₂releasing material and thus, results in CO₂ being released through thethermoplastic into the surrounding environment.

[0012] In one example, the CO₂ releasing material initiates CO₂production when the CO₂ releasing material is exposed to an elevatedrelative humidity of about at least 50% (measureed at 22C). In yetanother example, when the CO₂ releasing material is exposed toincreasing temperatures, the CO₂ production/release increases. Amongother factors, it is understood that the CO₂ production/release ratesare effected by the amount and proportion of carbonate and acid in thecomposition. In addition, the production/release rates is also effectedby the MVTR of the thermoplastic, the exposure to a specific relativehumidity and/or temperature.

[0013] In one application, the introduction of CO₂ gas lowers theambient oxygen content within the package and thus, slows therespiration rate of natural and processed food products. In anotherexample, when CO₂ converts to carbonic acid in the presence of moistureon the surface of a product, the increased level of carbonic acid on thesurface of the product decreases the pH. As a consequence, bacteriumthat is sensitive to higher acidic levels are inhibited. In a furtherexample, the increase in CO₂ gas reduces the overall oxygen content inthe package and thus, the amount of oxidation and/or oxygen sensitivebacterium.

[0014] In one example of the above, the purpose of releasing CO₂ is toaccomplish modified atmosphere packaging. As such, the control of theamount of CO₂ into the surrounding environment is used to achieve theoptimum shelf life—the lowest amount of oxygen concentration beforeanaerobic respiration is initiated.

[0015] Examples of products that may be protected by the presentinvention include, but are not limited to, natural and processed foodproducts such as cheese, luncheon meats, bacon, fermented diaryproducts, fruits and vegetables, raw meats, poultry, fresh and saltedfish, intermediate moisture foods (such as jerky, pet foods, and granolabars), high fat moist bakery products, acidified dairy products,mayonnaise and salad dressings, controlled atmosphere/modifiedatmosphere refrigerated extended shelf life foods (such as partiallycooked meals, pasta dishes, sauces, cut fruit, and vegetable salads, andother water-bearing foods).

[0016] In yet another embodiment, the present invention may be used fora CO₂ releasing article in the following products. For example, in oneillustrative example, the CO₂ releasing composition maintains anenvironment for fresh cut apples so as to maintain their texture andfirmness at about 30-45% CO₂ and, optionally, also results in an O₂level of about 2-5%. After about 24-hours of packaging the produce, theCO₂ releasing composition maintains an environment for fresh cut applesat a gas level of below about concentrations of 20% CO₂ and 5% O₂.

[0017] In another illustrative example, the CO₂ releasing compositionmaintains an environment for fresh cut lettuce so as to maintain theirtexture and firmness at below about 5% CO₂ and, optionally, also resultsin an O₂ level of about 2-5%, more particularly maintaining a O₂concentration above about 2%.

[0018] In one example, the CO₂ releasing composition is integrated intoa CO₂ releasing film into a package with barrier properties that canmaintain the desired gas concentrations. Suitable barrier films include,but are not limited to, films having selective permeation to O₂ and CO₂(e.g. a barrier film with a Beta value of less than about 1 where Betais defined as the ratio of CO₂ and O₂ transmission in a film material).

[0019] In yet another illustrative example, the CO₂ releasingcomposition maintains an environment for warm baked goods so as torelease CO₂ to slow aerobic respiration of organisms that may cause thebakery good to become stale. In addition, an absorbing material (e.g. adesiccant) may be incorporated into the composition to absorbdetrimental levels of moisture.

[0020] In yet another example, the present invention may be incorporatedinto packages for the fresh flower market (retail and wholesalerefrigerated cases). For example, elevated CO₂ levels have been found tomaintain the green color of flower stems. In one specific example, thepresent invention may be incorporated into a film or incorporated/addedto the present package that releases over a specified time period (e.g.30 day period).

[0021] In another example, the present invention may be incorporatedinto packages for fresh or frozen seafood (e.g. frozen/thawed case readyseafood). For example, the CO₂ releasing composition produces sufficientCO₂ to elevate the CO₂ concentration in the package and, as such, slowsaerobic respiration—while preventing anaerobic respiration. For example,the CO₂ releasing composition produces sufficient CO₂ to elevate the CO₂concentration in the package to above about 30% with an ambient O₂concentration of about 20% so as to slow the degradation of finnedseafood. In another example, the CO₂ releasing composition producessufficient CO₂ to elevate the CO₂ concentration in the package at aminimum of about 20% and the O₂ at about 20% to slow the growth of microorganisms on seafood. Under conventional conditions, Class A seafood canbe sold up to 7 days from the catch and Class B seafood can be sold 8-14days from the catch. It is believed that the conditions discussed abovewill result in extending the length of Class A seafood up to 10 days.

[0022] In another embodiment, the CO₂ releasing composition producessufficient CO₂ to in a film form over a specified time (e.g. 7 dayperiod) so as to maintains a gas environment of about 40% CO₂, 40%nitrogen and 20% oxygen.

[0023] In yet another embodiment, the present invention may alsoinclude, in addition to the CO₂ releasing composition that isincorporated within a thermoplastic, other components such as, but notlimited to, a biologically active ingredient such as a biocide (e.g.chlorine dioxide), and/or a desiccant. For example, a biocide may beincorporated into the CO₂ releasing composition that produces sufficientCO₂ so as to result in a modified atmosphere of about 30% CO₂, about 20%O₂ and about 50% N₂ to increase the shelf life of seafood.

[0024] In a further example, the present invention may be incorporatedinto packages for fresh fruits and/or vegetables. In one specificexample, this product would release over about a 14 day period. In yetanother example, the present invention may be incorporated into packagesfor the produce market. In one specific example, the present inventionwould be incorporated into bulk shipment of products like shreddedlettuce and berries.

[0025] In one example, typically, berries are bulk packaged and treatedwith CO₂ gas to elevate the CO₂ concentration in shipping containers.However, when the berries are removed from the bulk containers, gaslevels typically are not maintained. Berries respire and produce CO₂after harvesting. In one example, the CO₂ releasing composition isincorporated into a film in a single unit packages for berries andmaintains an environment for berries so as to elevate the CO₂ level inthe package (e.g. maintaining a CO₂ concentration of about 8-25%, mostparticularly at about 10-20%, in the package).

[0026] In another example, the present invention may be incorporatedinto packages for the meat. In one specific example, the presentinvention would be incorporated into both films to place insiderefrigerated display cases and labels to be inserted into case readypackages of meat.

[0027] In another embodiment, the proper selection of the thermoplasticand the resulting CO₂ composition with the desired level of CO₂permeability will allow packages according to the present invention tomaintain the desired steady state levels of that gas within the package.In producing the composition of the invention, the steady state levelsfor CO₂ within the packages are determined by, at least, the followingconsiderations: a) the permeability of the film; b) the volume of theheadspace of the package; and c) the respiration rate and quantity ofthe desired material (e.g. fruit, seafood). The permeability of the filmis determined by the characteristics of the film and the partialpressure gradients for the carbon dioxide across the film. The greaterthe partial pressure gradient between the package and the ambientenvironment outside the package for the gas, the greater the fluxtherein or thereout.

[0028] Whereas particular embodiments of the present invention have beendescribed above as examples, it will be appreciated that variations ofthe details may be made without departing from the scope of theinvention. One skilled in the art will appreciate that the presentinvention can be practiced by other than the disclosed embodiments, allof which are presented in this description for purposes of illustrationand not of limitation. It is noted that equivalents of the particularembodiments discussed in this description may practice the invention aswell. Therefore, reference should be made to the appended claims ratherthan the foregoing discussion of examples when assessing the scope ofthe invention in which exclusive rights are claimed.

What is claimed:
 1. A composition comprising a thermoplastic and a CO₂ releasing material; wherein the CO₂ releasing material comprises: a) a carbon and oxygen containing salt of an alkali or alkaline earth metal; and b) an acid; the CO₂ releasing material has a sufficient amount and ratio of the carbon and oxygen containing salt of the alkali or alkaline earth metal and the acid so that, in the presence of water, the CO₂ releasing material reacts to release CO₂ gas through the thermoplastic into a surrounding environment.
 2. The composition of claim 1 wherein the carbon and oxygen containing salt of an alkali or alkaline earth metal is a carbonate.
 3. The composition of claim 2 wherein the composition is in the form of a film, sheet, insert or liner.
 4. The composition of claim 2 wherein the CO₂ releasing material reacts and releases CO₂ gas through the thermoplastic into a package environment when the CO₂ releasing material is exposed to an elevated relative humidity of the package environment of about at least 50%, as measured at 22C.
 5. The composition of claim 2 wherein the CO₂ releasing composition maintains a package environment for cut apples at about 30-45% CO₂.
 6. The composition of claim 5 wherein the O₂ level is about 2-5%.
 7. The composition of claim 2 wherein the CO₂ releasing composition maintains a package environment for cut lettuce at below about 5% CO₂.
 8. The composition of claim 7 wherein the O₂ level is about 2-5%.
 9. The composition of claim 2 wherein the CO₂ releasing composition maintains a package environment for baked goods at a sufficient release rate of CO₂ to slow aerobic respiration of organisms that causes the baked good to become stale.
 10. The composition of claim 9 wherein an absorbing material is incorporated into the composition to absorb detrimental levels of moisture.
 11. The composition of claim 2 wherein the CO₂ releasing composition maintains a package environment for cut flowers market at a sufficient release rate of CO₂ to maintain the green color of flower stems for at least 30 days.
 12. The composition of claim 2 wherein the CO₂ releasing composition maintains a package environment for fresh or frozen seafood so as to produce sufficient CO₂ to slow aerobic respiration while reducing anaerobic respiration.
 13. The composition of claim 12 wherein the CO₂ releasing composition maintains a package environment for fresh or frozen seafood above about 30% with an ambient O₂ concentration of about 20%.
 14. The composition of claim 12 wherein the CO₂ releasing composition maintains a package environment for fresh or frozen seafood at an elevated CO₂ concentration of at least about 20% and the O₂ concentration at about 20%.
 15. The composition of claim 2 wherein a biologically active ingredient is incorporated into the composition.
 16. The composition of claim 15 wherein the biologically active ingredient is chlorine dioxide and added in sufficient amounts with the CO₂ releasing material so as to produce a modified atmosphere of about 30% CO₂, about 20% O₂ and about 50% N₂ for seafood.
 17. The composition of claim 2 wherein the CO₂ releasing composition is integrated into a CO₂ releasing film into a package with a barrier film having selective permeation to O₂ and CO₂.
 18. The composition of claim 2 wherein the CO₂ releasing composition produces a sufficient amount of CO₂ in a film form so as to maintains a gas environment in the package of about 40% CO₂, 40% nitrogen and 20% oxygen. 